const jokeEl = document.getElementById('joke');
const jokeBtn = document.getElementById('joke-btn');

const xhr = new XMLHttpRequest();
xhr.open('GET', 'https://api.chucknorris.io/jokes/random',true);
xhr.onreadystatechange = function () {
 if (this.readyState === 4) {
 if (this.status === 200) {
 const joke = JSON.parse(this.responseText).value;
 jokeEl.innerHTML = joke;
 } else {
 jokeEl.innerHTML = '出现错误，不好笑。';
 }
 }
};
xhr.send();
jokeBtn.addEventListener('click', generateJoke);
document.addEventListener('DOMContentLoaded', generateJoke);